The association between the Hawaiian squid Euprymna scolopes and the bioluminescent bacterium Vibrio fischeri provides a model system to study the signal exchange between a prokaryote and a eukaryote during establishment of symbiosis. The hybrid sensor kinase RscS of V. fischeri is required for the initiation of symbiosis. As part of a two component regulatory system, RscS likely receives a colonization signal and transmits this signal to a response regulator, ultimately resulting in successful colonization of the squid. This work will examine the structure of RscS to determine the region(s) of the protein required for detection of the colonization signal. [unreadable] [unreadable]